Chronic stress induces mast cell-dependent bacterial adherence and initiates mucosal inflammation in rat intestine

Psychoneuroimmunology: the experiential dimension

Accumulating evidence has made clear that experience--the knowledge an individual acquires during a lifetime of sensing and acting--is of fundamental biological relevance. Experience makes an impact on all adaptive systems, including the endocrine, immune, and nerve systems, and is of the essence, not only for the unfolding of an organisms' healthy status, but also for the development of malfunctional traits. Nevertheless, experience is often excluded from empirical approaches. A variety of complex interactions that influence life histories are thereby neglected. Such ignorance is especially detrimental for psychoneuroimmunology, the science that seeks to understand how the exquisite and dynamic interplay between mind, body, and environment relates to behavioral characteristics. The article reviews claims for incorporating experience as a member of good explanatory standing in biology and medicine, and more specifically, claims that experiential knowledge is required to enable meaningful and relevant explanations and predictions in the psychoneuroimmunological realm.

Role of nociceptin/orphanin FQ receptors in the decrease of mucosal mast cells caused by acute stress in the rat colon

AIMS

Mucosal mast cells (MMC) are mediators of the stress responses in the gastrointestinal tract. We examined the effect of acute cold-restraint stress and of the neuropeptide nociceptin/orphanin FQ (N/OFQ), implicated in the modulation of stress responses, on MMC density in the rat colon.

MAIN METHODS

Stress was induced by restraining the animals into individual cages at 3°C for 3h. N/OFQ and the selective N/OFQ peptide (NOP) receptor antagonist, UFP-101, were infused subcutaneously via Alzet osmotic minipumps. Segments of the distal colon were collected. MMCs were identified immunohistochemically with a monoclonal antibody to rat mast cell protease (RMCP) II and with a rabbit polyclonal antibody to CD117/c-kit receptor.

KEY FINDINGS

Acute stress caused a decrease in the density of MMCs in the rat colonic mucosa. Short-term peripheral infusion of N/OFQ (0.1 to 10 μg/kg/h for 4h) caused a dose-related reduction of MMC density. Peak reduction occurred after the 4-h infusion of N/OFQ, 1 μg/kg/h. Reduction was maintained after the 52-h infusion period and declined following 7 and 14 days of infusion. The infusion of N/OFQ (1μg/kg/h for 4h) in rats exposed to acute stress caused a decrease in MMC density comparable to that obtained with the single treatments. UFP-101, at the doses of 1 and 10 μg/kg/h, which itself had no significant effect on MMC density, when concurrently infused in stress-exposed rats, abolished the stress-induced decrease of MMC density.

SIGNIFICANCE

Present results indicate that the peripheral N/OFQ-NOP system is involved in stress-induced reduction of MMC density.

Intestinal epithelial barrier dysfunction in food hypersensitivity

Intestinal epithelial barrier plays a critical role in the maintenance of gut homeostasis by limiting the penetration of luminal bacteria and dietary allergens, yet allowing antigen sampling for the generation of tolerance. Undigested proteins normally do not gain access to the lamina propria due to physical exclusion by tight junctions at the cell-cell contact sites and intracellular degradation by lysosomal enzymes in enterocytes. An intriguing question then arises: how do macromolecular food antigens cross the epithelial barrier? This review discusses the epithelial barrier dysfunction in sensitized intestine with special emphasis on the molecular mechanism of the enhanced transcytotic rates of allergens. The sensitization phase of allergy is characterized by antigen-induced cross-linking of IgE bound to high affinity FcεRI on mast cell surface, leading to anaphylactic responses. Recent studies have demonstrated that prior to mast cell activation, food allergens are transported in large quantity across the epithelium and are protected from lysosomal degradation by binding to cell surface IgE and low-affinity receptor CD23/FcεRII. Improved immunotherapies are currently under study including anti-IgE and anti-CD23 antibodies for the management of atopic disorders.

Is metabolic stress a common denominator in inflammatory bowel disease?

The enteric epithelium represents the major boundary between the outside world and the body, and in the colon it is the interface between the host and a vast and diverse microbiota. A common feature of inflammatory bowel disease (IBD) is decreased epithelial barrier function, and while a cause-and-effect relationship can be debated, prolonged loss of epithelial barrier function (whether this means the ability to sense bacteria or exclude them) would contribute to inflammation. While there are undoubtedly individual nuances in IBD, we review data in support of metabolic stress--that is, perturbed mitochondrial function--in the enterocyte as a contributing factor to the initiation of inflammation and relapses in IBD. The postulate is presented that metabolic stress, which can arise as a consequence of a variety of stimuli (e.g., infection, bacterial dysbiosis, and inflammation also), will reduce epithelial barrier function and perturb the enterocyte-commensal flora relationship and suggest that means to negate enterocytic metabolic stress should be considered as a prophylactic or adjuvant therapy in IBD.

Captivity induces hyper-inflammation in the house sparrow (Passer domesticus)

Some species thrive in captivity but others exhibit extensive psychological and physiological deficits, which can be a challenge to animal husbandry and conservation as well as wild immunology. Here, we investigated whether captivity duration impacted the regulation of a key innate immune response, inflammation, of a common wild bird species, the house sparrow (Passer domesticus). Inflammation is one of the most commonly induced and fast-acting immune responses animals mount upon exposure to a parasite. However, attenuation and resolution of inflammatory responses are partly coordinated by glucocorticoid hormones, hormones that can be disregulated in captivity. Here, we tested whether captivity duration alters corticosterone regulation and hence the inflammatory response by comparing the following responses to lipopolysaccharide (LPS; a Gram-negative bacteria component that induces inflammation) of birds caught wild and injected immediately versus those held for 2 or 4 weeks in standard conditions: (1) the magnitude of leukocyte immune gene expression [the cytokines, interleukin 1β and interleukin 6, and Toll-like receptor 4 (TLR4)], (2) the rate of clearance of endotoxin, and (3) the release of corticosterone (CORT) in response to endotoxin (LPS). We predicted that captivity duration would increase baseline CORT and thus suppress gene expression and endotoxin clearance rate. However, our predictions were not supported: TLR4 expression increased with time in captivity irrespective of LPS, and cytokine expression to LPS was stronger the longer birds remained captive. Baseline CORT was not affected by captivity duration, but CORT release post-LPS occurred only in wild birds. Lastly, sparrows held captive for 4 weeks maintained significantly higher levels of circulating endotoxin than other groups, perhaps due to leakage of microbes from the gut, but exogenous LPS did not increase circulating levels over the time scale samples were collected. Altogether, captivity appears to have induced a hyper-inflammatory state in house sparrows, perhaps due to disregulation of glucocorticoids, natural microflora or both.

Stress-related alterations of visceral sensation: animal models for irritable bowel syndrome study

Stressors of different psychological, physical or immune origin play a critical role in the pathophysiology of irritable bowel syndrome participating in symptoms onset, clinical presentation as well as treatment outcome. Experimental stress models applying a variety of acute and chronic exteroceptive or interoceptive stressors have been developed to target different periods throughout the lifespan of animals to assess the vulnerability, the trigger and perpetuating factors determining stress influence on visceral sensitivity and interactions within the brain-gut axis. Recent evidence points towards adequate construct and face validity of experimental models developed with respect to animals' age, sex, strain differences and specific methodological aspects such as non-invasive monitoring of visceromotor response to colorectal distension as being essential in successful identification and evaluation of novel therapeutic targets aimed at reducing stress-related alterations in visceral sensitivity. Underlying mechanisms of stress-induced modulation of visceral pain involve a combination of peripheral, spinal and supraspinal sensitization based on the nature of the stressors and dysregulation of descending pathways that modulate nociceptive transmission or stress-related analgesic response.

Small bowel homing T cells are associated with symptoms and delayed gastric emptying in functional dyspepsia

OBJECTIVES

Immune activation may have an important pathogenic role in the irritable bowel syndrome (IBS). While little is known about immunologic function in functional dyspepsia (FD), we have observed an association between cytokine secretion by peripheral blood mononuclear cells (PBMCs) and symptoms in IBS. Upper gastrointestinal inflammatory diseases are characterized by enhanced small bowel homing α4-, β7-integrin, chemokine receptor 9 (CCR9) positive T lymphocytes. We hypothesized that increased cytokine release and elevated circulating small bowel homing T cells are linked to the severity of symptoms in patients with FD. Thus, we aimed to (i) compare cytokine release in FD and healthy controls (HCs), (ii) quantify "gut homing" T cells in FD compared with HC and patients with IBS, and (iii) correlate the findings to symptom severity and gastric emptying.

METHODS

PBMC from 45 (Helicobacter pylori negative) patients with FD (Rome II) and 35 matched HC were isolated by density gradient centrifugation and cultured for 24 h. Cytokine production (tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-10) was measured by enzyme-linked immunosorbent assay. CD4+ α4β7+CCR9+ T cells were quantified by flow cytometry in FD, HC and 23 patients with IBS. Gastric emptying was measured by scintigraphy. Symptom severity was assessed utilizing the standardized Gastrointestinal Symptom Score.

RESULTS

FD patients had significantly higher TNF-α (107.2 ± 42.8 vs. 58.7 ± 7.4 pg/ml), IL-1β (204.8 ± 71.5 vs. 80.2 ± 17.4 pg/ml), and IL-10 (218 ± 63.3 vs. 110.9 ± 18.5 pg/ml) levels compared with HC, and enhanced gut homing lymphocytes compared with HC or IBS. Cytokine release and CD4+α4β7+CCR9+ lymphocytes were correlated with the symptom intensity of pain, cramps, nausea, and vomiting. Delayed gastric emptying was significantly associated (r = 0.78, P = 0.021) with CD4+α4β7+CCR9+ lymphocytes and IL-1β, TNF-α, and IL-10 secretion.

CONCLUSIONS

Cellular immune activation with increased small bowel homing T cells may be key factors in the clinical manifestations of H. pylori-negative FD.

Immune function and HPA axis activity in free-ranging rhesus macaques

In mammals, the hypothalamic-pituitary-adrenal (HPA) axis and immune system play an important role in the maintenance of homeostasis. Dysregulation of either system resulting, for example, from psychosocial or reproductive stress increases susceptibility to disease and mortality risk, especially in aging individuals. In a study of free-ranging rhesus macaques, we examined how female age, reproductive state, social rank, and body condition influence (i) aspects of cytokine biology (plasma concentrations of interleukin-1 receptor antagonist (IL-1ra), IL-6 and IL-8), and (ii) HPA axis activity (plasma and fecal glucocorticoid levels). We also assessed individual differences in cytokine and hormone concentrations over time to determine their consistency and to investigate relations between these two indicators of physiological regulation and demand. Female monkeys showed marked increases in HPA axis activity during pregnancy and lactation, and increased circulating levels of IL-1ra with advancing age. Inter-individual differences in IL-1ra and IL-8 were consistent over successive years, suggesting that both are stable, trait-like characteristics. Furthermore, the concentrations of fecal glucocorticoid hormones in non-pregnant, non-lactating females were correlated with their plasma cortisol and IL-8 concentrations. Some individuals showed permanently elevated cytokine levels or HPA axis activity, or a combination of the two, suggesting chronic stress or disease. Our results enhance our understanding of within- and between-individual variation in cytokine levels and their relationship with glucocorticoid hormones in free-ranging primates. These findings can provide the basis for future research on stress and allostatic load in primates.

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Eosinophils express muscarinic receptors and corticotropin-releasing factor to disrupt the mucosal barrier in ulcerative colitis

BACKGROUND & AIMS

Altered intestinal barrier function has been implicated in the pathophysiology of ulcerative colitis (UC) in genetic, functional, and epidemiological studies. Mast cells and corticotropin-releasing factor (CRF) regulate the mucosal barrier in human colon. Because eosinophils are often increased in colon tissues of patients with UC, we assessed interactions among mast cells, CRF, and eosinophils in the mucosal barrier of these patients.

METHODS

Transmucosal fluxes of protein antigens (horseradish peroxidase) and paracellular markers ((51)Cr-EDTA, fluorescein isothiocyanate-dextran 4000) were studied in noninflamed, colonic mucosal biopsy samples collected from 26 patients with UC and 53 healthy volunteers (controls); samples were mounted in Ussing chambers. We also performed fluorescence and electron microscopy of human tissue samples, assessed isolated eosinophils, and performed mechanistic studies using in vitro cocultured eosinophils (15HL-60), mast cells (HMC-1), and a colonic epithelial cell line (T84).

RESULTS

Colon tissues from patients with UC had significant increases in permeability to protein antigens compared with controls. Permeability was blocked by atropine (a muscarinic receptor antagonist), α-helical CRF(9-41) (a CRF receptor antagonist), and lodoxamide (a mast-cell stabilizer). Eosinophils were increased in number in UC tissues (compared with controls), expressed the most M2 and M3 muscarinic receptors of any mucosal cell type, and had immunoreactivity to CRF. In coculture studies, carbachol activation of eosinophils caused production of CRF and activation of mast cells, which increased permeability of T84 epithelial cells to macromolecules.

CONCLUSIONS

We identified a neuroimmune intercellular circuit (from cholinergic nerves, via eosinophils to mast cells) that mediates colonic mucosal barrier dysfunction in patients with UC. This circuit might exacerbate mucosal inflammation.

Long-term peripheral infusion of nociceptin/orphanin FQ promotes hyperplasia, activation and migration of mucosal mast cells in the rat gastric fundus

The endogenous neuropeptide nociceptin/orphanin FQ (N/OFQ) modulates behavioral and gastrointestinal responses to stress. Mucosal mast cells (MMCs) are primary mediators of stress-related responses in the gastrointestinal tract. We investigated the influence of N/OFQ and of the N/OFQ peptide (NOP) receptor antagonist, UFP-101, on MMCs in the rat gastric fundus. N/OFQ was infused subcutaneously for 52 h at 0.1, 1 and 10 μg/kg/h and at 1 μg/kg/h for 4h, 52 h, 7 days and 14 days via Alzet osmotic minipumps. Density of MMCs and connective tissue mast cells (CTMCs) was assessed histochemically and immunohistochemically. Activation and location of MMCs were assessed by transmission electron microscopy. Contacts between MMCs and nerve elements were assessed by double immunofluorescence. N/OFQ (1 μg/kg/h) and UFP-101 (10 and 30 μg/kg/h) were infused subcutaneously in the absence and presence of acute cold-restraint stress and density of MMCs was assessed. Peripheral N/OFQ dose-dependently increased the density of MMCs, while not influencing CTMCs. The increasing effect was maintained up to 14 days following continuous infusion, while after termination of the 4-h infusion, the effect declined rapidly. The peptide promoted the activation of MMCs and their migration from the lamina propria toward the epithelial layer. The association between MMCs and nerve fibers was time-dependently down-regulated following N/OFQ infusion. The stress-induced hyperplasia of MMCs was not influenced by N/OFQ and abolished by UFP-101. UFP-101 alone was ineffective. The present results suggest that endogenous N/OFQ could be considered a potential component of the circuit neuropeptides-mast cells-stress.

The microbiome-gut-brain axis: from bowel to behavior

The ability of gut microbiota to communicate with the brain and thus modulate behavior is emerging as an exciting concept in health and disease. The enteric microbiota interacts with the host to form essential relationships that govern homeostasis. Despite the unique enteric bacterial fingerprint of each individual, there appears to be a certain balance that confers health benefits. It is, therefore, reasonable to note that a decrease in the desirable gastrointestinal bacteria will lead to deterioration in gastrointestinal, neuroendocrine or immune relationships and ultimately disease. Therefore, studies focusing on the impact of enteric microbiota on the host and in particular on the central nervous system are essential to our understanding of the influence of this system. Recent studies published in this Journal demonstrate that germ-free mice display alterations in stress-responsivity, central neurochemistry and behavior indicative of a reduction in anxiety in comparison to conventional mice. Such data offer the enticing proposition that specific modulation of the enteric microbiota may be a useful strategy for stress-related disorders and for modulating the co-morbid aspects of gastrointestinal disorders such as irritable bowel syndrome and inflammatory bowel disease.

The brain-gut axis in abdominal pain syndromes

The importance of bidirectional brain-gut interactions in gastrointestinal (GI) illness is increasingly recognized, most prominently in the area of functional GI syndromes such as irritable bowel syndrome (IBS), functional dyspepsia, and functional chest pain. The brain receives a constant stream of interoceptive input from the GI tract, integrates this information with other interoceptive information from the body and with contextual information from the environment, and sends an integrated response back to various target cells within the GI tract. This system is optimized to assure homeostasis of the GI tract during physiological perturbations and to adapt GI function to the overall state of the organism. In health, the great majority of interoceptive information reaching the brain is not consciously perceived but serves primarily as input to autonomic reflex pathways. In patients with functional abdominal pain syndromes, conscious perception of interoceptive information from the GI tract, or recall of interoceptive memories of such input, can occur in the form of constant or recurrent discomfort or pain. This is often associated with alterations in autonomic nervous system output and with emotional changes. A model is proposed that incorporates reported peripheral and central abnormalities in patients with IBS, extrapolates similar alterations in brain-gut interactions to patients with other chronic abdominal pain syndromes, and provides novel treatment targets.

Importance of disrupted intestinal barrier in inflammatory bowel diseases

The current paradigm of inflammatory bowel diseases (IBD), both Crohn's disease (CD) and ulcerative colitis (UC), involves the interaction between environmental factors in the intestinal lumen and inappropriate host immune responses in genetically predisposed individuals. The intestinal mucosal barrier has evolved to maintain a delicate balance between absorbing essential nutrients while preventing the entry and responding to harmful contents. In IBD, disruptions of essential elements of the intestinal barrier lead to permeability defects. These barrier defects exacerbate the underlying immune system, subsequently resulting in tissue damage. The epithelial phenotype in active IBD is very similar in CD and UC. It is characterized by increased secretion of chloride and water, leading to diarrhea, increased permeability via both the transcellular and paracellular routes, and increased apoptosis of epithelial cells. The main cytokine that seems to drive these changes is tumor necrosis factor alpha in CD, whereas interleukin (IL)-13 may be more important in UC. Therapeutic restoration of the mucosal barrier would provide protection and prevent antigenic overload due to intestinal "leakiness." Here we give an overview of the key players of the intestinal mucosal barrier and review the current literature from studies in humans and human systems on mechanisms underlying mucosal barrier dysfunction in IBD.

Intestinal barrier function of Atlantic salmon (Salmo salar L.) post smolts is reduced by common sea cage environments and suggested as a possible physiological welfare indicator

Background

Fish farmed under high intensity aquaculture conditions are subjected to unnatural environments that may cause stress. Therefore awareness of how to maintain good health and welfare of farmed fish is important. For Atlantic salmon held in sea cages, water flow, dissolved oxygen (DO) levels and temperature will fluctuate over time and the fish can at times be exposed to detrimentally low DO levels and high temperatures. This experimental study investigates primary and secondary stress responses of Atlantic salmon post smolts to long-term exposure to reduced and fluctuating DO levels and high water temperatures, mimicking situations in the sea cages. Plasma cortisol levels and cortisol release to the water were assessed as indicators of the primary stress response and intestinal barrier integrity and physiological functions as indicators of secondary responses to changes in environmental conditions.

Results

Plasma cortisol levels were elevated in fish exposed to low (50% and 60% saturation) DO levels and low temperature (9°C), at days 9, 29 and 48. The intestinal barrier function, measured as electrical resistance (TER) and permeability of mannitol at the end of the experiment, were reduced at 50% DO, in both proximal and distal intestine. When low DO levels were combined with high temperature (16°C), plasma cortisol levels were elevated in the cyclic 1:5 h at 85%:50% DO group and fixed 50% DO group compared to the control (85% DO) group at day 10 but not at later time points. The intestinal barrier function was clearly disturbed in the 50% DO group; TER was reduced in both intestinal regions concomitant with increased paracellular permeability in the distal region.

Conclusions

This study reveals that adverse environmental conditions (low water flow, low DO levels at low and high temperature), that can occur in sea cages, elicits primary and secondary stress responses in Atlantic salmon post smolts. The intestinal barrier function was significantly affected by prolonged hypoxic stress even when no primary stress response was observed. This suggests that intestinal barrier function is a good experimental marker for evaluation of chronic stress and that it can be a valuable tool to study the impact of various husbandry conditions on health and welfare of farmed Atlantic salmon.

Chronological assessment of mast cell-mediated gut dysfunction and mucosal inflammation in a rat model of chronic psychosocial stress

Life stress and mucosal inflammation may influence symptom onset and severity in certain gastrointestinal disorders, particularly irritable bowel syndrome (IBS), in connection with dysregulated intestinal barrier. However, the mechanism responsible remains unknown. Crowding is a validated animal model reproducing naturalistic psychosocial stress, whose consequences on gut physiology remain unexplored. Our aims were to prove that crowding stress induces mucosal inflammation and intestinal dysfunction, to characterize dynamics in time, and to evaluate the implication of stress-induced mast cell activation on intestinal dysfunction. Wistar-Kyoto rats were submitted to 15 days of crowding stress (8 rats/cage) or sham-crowding (2 rats/cage). We measured spontaneous and corticotropin-releasing factor-mediated release of plasma corticosterone. Stress-induced intestinal chrono-pathobiology was determined by measuring intestinal inflammation, epithelial damage, mast cell activation and infiltration, and intestinal barrier function. Corticosterone release was higher in crowded rats throughout day 15. Stress-induced mild inflammation, manifested earlier in the ileum and the colon than in the jejunum. While mast cell counts remained mostly unchanged, piecemeal degranulation increased along time, as the mucosal content and luminal release of rat mast cell protease-II. Stress-induced mitochondrial injury and increased jejunal permeability, both events strongly correlated with mast cell activation at day 15. Taken together, we have provided evidences that long-term exposure to psychosocial stress promotes mucosal inflammation and mast cell-mediated barrier dysfunction in the rat bowel. The notable resemblance of these findings with those in some IBS patients, support the potential interest and translational validity of this experimental model for the research of stress-sensitive intestinal disorders, particularly IBS.

The enteric nervous system as a regulator of intestinal epithelial barrier function in health and disease

The intestinal epithelia proliferate and differentiate along the crypt villus axis to constitute a barrier cell layer separating some 10¹³ potentially harmful bacteria from a sterile mucosal compartment. Strict regulatory mechanisms are required to maintain a balance between the appropriate uptake of luminal food components and proteins, while constraining the exposure of the mucosal compartment to luminal antigens and microbes. The enteric nervous system is increasingly recognized as such a regulatory housekeeper of the epithelial barrier integrity, in addition to its ascribed immunomodulatory potential. Inflammation affects both epithelial integrity and barrier function and, in turn, loss of barrier function perpetuates inflammatory conditions. The observation that inflammatory conditions affect enteric neurons may add to the dysregulated barrier function in chronic disease. Here, we review the current understanding of the regulatory role of the nervous system in the maintenance of barrier function in healthy state, or during pathological conditions of, for instance, stress-induced colitis, surgical trauma or inflammation. We will discuss the clinical potential for advances in understanding the role of the enteric nervous system in this important phenomenon.

Probiotics and the gut microbiota in intestinal health and disease

The use of probiotics is increasing in popularity for both the prevention and treatment of a variety of diseases. While a growing number of well-conducted, prospective, randomized, controlled, clinical trials are emerging and investigations of underlying mechanisms of action are being undertaken, questions remain with respect to the specific immune and physiological effects of probiotics in health and disease. This Review considers recent advances in clinical trials of probiotics for intestinal disorders in both adult and pediatric populations. An overview of recent in vitro and in vivo research related to potential mechanisms of action of various probiotic formulations is also considered.

Functional changes induced by psychological stress are not enough to cause intestinal inflammation in Sprague-Dawley rats

BACKGROUND

It is well known that stress contributes to the perpetuation of several gastrointestinal diseases. However, its role as a trigger of the inflammatory process in absence of other putative contributing factors remains controversial. Our aim was to elucidate whether stress per se can induce a primary gut inflammation in non-predisposed rats.

METHODS

Male Sprague-Dawley rats were divided in sham and stress groups. Chronic stress was induced by subjecting animals 1 h day(-1) to wrap restraint or water avoidance stress alternatively for five consecutive days, as a model of ongoing life stress.

KEY RESULTS

Chronic stress induced a significant decrease in body weight gain without changes in food intake and an increase in frequency of defecation. Electromiografic (EMG) study showed that the duration of the migrating motor cycles (MMCs), but not its frequency, was shortened in stressed animals compared with non-stress conditions. Moreover, stressful stimulus caused mucosal mast cell hyperplasia and a decrease of iNOS mRNA expression. Bacterial translocation observed in stressed animals was not related to changes in epithelial barrier function and was not enough to induce intestinal inflammation.

CONCLUSIONS & INFERENCES

Decreased MMC duration, mast cell hyperplasia and decreased mRNA iNOS expression, but not altered epithelial barrier function, could be factors implicated in bacterial translocation-induced by chronic stress. However, these changes are not sufficient to induce intestinal inflammation in stress non-susceptible strain of rats.

Stress-induced barrier disruption of rat follicle-associated epithelium involves corticotropin-releasing hormone, acetylcholine, substance P, and mast cells

BACKGROUND

The follicle-associated epithelium (FAE) is specialized in uptake and sampling of luminal antigens and bacteria. We previously showed that stress increased FAE permeability in rats. An increased uptake may alter antigen exposure in Peyer's patches leading to intestinal disease. The aim of this study was to elucidate mechanisms involved in the acute stress-induced increase in FAE permeability.

METHODS

Rats were pretreated i.p. with corticotropin-releasing hormone receptor (CRH-R) antagonist, neurokinin receptor 1 (NK-1R) antagonist, atropine, the mast cell stabilizer doxantrazole (DOX), or NaCl, and submitted to 1-h acute water avoidance stress. FAE tissues were mounted in Ussing chambers for measurements of permeability to (51)Cr-EDTA, horseradish peroxidase (HRP) and chemically killed Escherichia coli K-12. Further, FAE segments were exposed in vitro in chambers to CRH, substance P (SP), carbachol, and DOX. Neurotransmitter- and receptor distribution was studied by immunohistochemistry.

KEY RESULTS

Stress-induced increases in uptake across FAE of HRP and E. coli were reduced by DOX, CRH-R antagonist and atropine, whereas the NK-1R antagonist decreased (51)Cr-EDTA permeability. Exposure to CRH and carbachol increased HRP and E. coli passage, whereas SP increased bacterial and (51)Cr-EDTA permeability. DOX counteracted all of these effects. Immunohistochemistry revealed CRH, acetylcholine, SP, and their receptors on mast cells within the Peyer's patches, subepithelial dome, and adjacent villi.

CONCLUSIONS & INFERENCES

Corticotropin-releasing hormone and acetylcholine signaling affect mainly transcellular permeability while SP seems more selective toward the paracellular pathways. Our findings may be of importance for the understanding of the pathogenesis of stress-related intestinal disorders.

Enhanced translocation of bacteria across metabolically stressed epithelia is reduced by butyrate

BACKGROUND

The gut microflora in some patients with Crohn's disease can be reduced in numbers of butyrate-producing bacteria and this could result in metabolic stress in the colonocytes. Thus, we hypothesized that the short-chain fatty acid, butyrate, is important in the maintenance and regulation of the barrier function of the colonic epithelium.

METHODS

Confluent monolayers of the human colon-derived T84 or HT-29 epithelial cell lines were exposed to dinitrophenol (DNP (0.1 mM), uncouples oxidative phosphorylation) + Escherichia coli (strain HB101, 10(6) cfu) +/- butyrate (3-50 mM). Transepithelial resistance (TER), and bacterial internalization and translocation were assessed over a 24-hour period. Epithelial ultrastructure was assessed by transmission electron microscopy.

RESULTS

Epithelia under metabolic stress display decreased TER and increased numbers of pseudopodia that is consistent with increased internalization and translocation of the E. coli. Butyrate (but not acetate) significantly reduced the bacterial translocation across DNP-treated epithelia but did not ameliorate the drop in TER in the DNP+E. coli exposed monolayers. Inhibition of bacterial transcytosis across metabolically stressed epithelia was associated with reduced I-kappaB phosphorylation and hence NF-kappaB activation.

CONCLUSIONS

Reduced butyrate-producing bacteria could result in increased epithelial permeability particularly in the context of concomitant exposure to another stimulus that reduces mitochondria function. We speculate that prebiotics, the substrate for butyrate synthesis, is a valuable prophylaxis in the regulation of epithelial permeability and could be of benefit in preventing relapses in IBD.

Repeated psychological stress-induced alterations of visceral sensitivity and colonic motor functions in mice: influence of surgery and postoperative single housing on visceromotor responses

Visceral pain modulation by chronic stress in mice has been little studied. Electromyography (EMG) recording of abdominal muscle contractions, as a proxy to the visceromotor response (VMR), requires electrode implantation and post-surgical single housing (SH) which could affect the VMR to stress. To test this hypothesis, male mice had electrode implantation surgery (S) plus SH, or no surgery and were group housed (NS-GH) or single housed (NS-SH) and exposed to either water avoidance stress (WAS, 1 h/day) or left undisturbed in their home cages for 10 days. The VMR to phasic ascending colorectal distension (CRD) was assessed before (basal) and 24 h after 10 days of WAS or no stress using a surgery-free method of intraluminal colonic pressure (ICP) recording (solid-state manometry). WAS heightened significantly the VMR to CRD at 30, 45, and 60 mmHg in S-SH vs. NS-GH, but not compared to NS-SH conscious mice. Compared to basal CRD, WAS increased VMR at 60 mmHg in the S-SH group and decreased it at 30-60 mmHg in NS-GH mice, while having no effect in NS-SH mice. The average defecation during the hour of repeated WAS over 10 days was 1.9 and 2.4 fold greater in S-SH vs. NS-GH and NS-SH mice, respectively. These data indicate that the combination of S-SH required for VMR monitoring with EMG is an important component of repeated WAS-induced post-stress visceral hypersensitivity and defecation in mice.

The intestinal barrier and its regulation by neuroimmune factors

BACKGROUND

The ability to control uptake across the mucosa and protect from damage of harmful substances from the lumen is defined as intestinal barrier function. A disturbed barrier dysfunction has been described in many human diseases and animal models, for example, inflammatory bowel disease, irritable bowel syndrome, and intestinal hypersensitivity. In most diseases and models, alterations are seen both of the paracellular pathway, via the tight junctions, and of the transcellular routes, via different types of endocytosis. Recent studies of pathogenic mechanisms have demonstrated the important role of neuroimmune interaction with the epithelial cells in the regulation of barrier function. Neural impulses from extrinsic vagal and/or sympathetic efferent fibers or intrinsic enteric nerves influence mucosal barrier function via direct effects on epithelial cells or via interaction with immune cells. For example, by nerve-mediated activation by corticotropin-releasing hormone or cholinergic pathways, mucosal mast cells release a range of mediators with effects on transcellular, and/or paracellular permeability (for example, tryptase, TNF-alpha, nerve growth factor, and interleukins).

PURPOSE

In this review, we discuss current physiological and pathophysiological aspects of the intestinal barrier and, in particular, its regulation by neuroimmune factors.

Antimicrobial anxiety: the impact of stress on antimicrobial immunity

Leukocytes and epithelial cells are fundamental to antimicrobial immunity. Their antimicrobial responses are an evolutionarily conserved component of the innate immune system and are influenced by the host's response to external stimuli. The efficacy of host defense via antimicrobial responses derives from the ability of AMPs to rapidly identify and eradicate foreign microbes and activate proinflammatory pathways, and from the capacity of later innate and adaptive immune responses to amplify protection through distinct biochemical mechanisms. Recent advances in neuroimmunology have identified a direct link between the neuroendocrine and immune systems, where environmental stimuli are generally believed to promote a transient effect on the immune system in response to environmental challenges and are presumably brought back to baseline levels via neuroendocrine pathways. Stress is an environmental stimulus that flares from a variety of circumstances and has become engrained in human society. Small bouts of stress are believed to enhance the host's immune response; however, prolonged periods of stress can be detrimental through excess production of neuroendocrine-derived mediators that dampen immune responses to invasive pathogens. Elucidation of the mechanisms behind stress-induced immune modulation of antimicrobial responses will ultimately lead to the development of more effective therapeutic interventions for pathologic conditions. It is the intent of this review to broaden the existing paradigm of how stress-related molecules dampen immune responses through suppression of antimicrobial mechanisms, and to emphasize that bacteria can use these factors to enhance microbial pathogenesis during stress.

Alterations in colonic corticotropin-releasing factor receptors in the maternally separated rat model of irritable bowel syndrome: differential effects of acute psychological and physical stressors

Early-life stress is a key predisposing factor to the development of functional gastrointestinal (GI) disorders. Thus, changes in stress-related molecular substrates which influence colonic function may be important in understanding the pathophysiology of such disorders. Activation of peripheral corticotropin-releasing factor (CRF) receptors is thought to be important in the maintenance of GI function homeostasis. Therefore, immunofluorescent and Western blotting techniques were utilized to investigate colonic expression of CRF receptors in the maternal separation (MS) model as compared to non-separated (NS) rats. Receptor expression was also assessed following exposure to two different acute stressors, the open field (OF) and colorectal distension (CRD). Immunofluorescent dual-labeling demonstrated increased activation of both CRFR1 (MS: 79.6+/-4.4% vs. NS: 43.8+/-6.8%, p<0.001) and CRFR2 (MS: 65.9+/-3.2% vs. NS: 51.6+/-5.8%, p<0.05) positive cells in MS rats. Protein expression of CRFR1 and CRFR2 in the proximal colon was similar under baseline conditions and not affected by exposure to an OF stressor in either cohort. In contrast, distal CRFR1 and CRFR2 levels were higher in MS rats but were significantly reduced post OF stress. Moreover, decreases in expression of CRFR1 in the proximal and distal colon of NS rats following exposure to CRD were blunted in MS rats. CRD also caused an increase in the functional isoform of CRFR2 in the distal colon of MS rats with no effect in NS colons. This study demonstrates that acute stressors alter colonic CRF receptor expression in a manner that is determined by the underlying stress sensitivity of the subject.

Intestinal permeability in irritable bowel syndrome patients: effects of NSAIDs

Intestinal permeability and the effect of NSAIDs on permeability were investigated in 14 irritable bowel syndrome (IBS) patients and 15 healthy subjects. In the study, 24-h urinary recoveries of orally administered polyethylene glycols (PEGs 400, 1500, and 4000) were not significantly different in healthy subjects and IBS patients before or after NSAID ingestion. Lactulose mannitol ratios in healthy subjects and IBS patients were not significantly different. Only time-dependent monitoring of PEG excretion showed that NSAIDs enhanced intestinal permeability for PEG 4000 in healthy subjects (P = 0.050) and for PEGs 400, 1500, and 4000 in IBS patients (P = 0.012, P = 0.041, and P = 0.012, respectively). These results show that intestinal permeability in IBS patients is not different from that in healthy subjects; NSAIDs compromise intestinal permeability in IBS patients to a greater extent than in healthy subjects, which suggests that IBS is associated with an altered response of the intestinal barrier to noxious agents.

Distinct alterations in colonic morphology and physiology in two rat models of enhanced stress-induced anxiety and depression-like behaviour

Stress and anxiety are important causal and exacerbating factors in functional gastro-intestinal (GI) disorders such as irritable bowel syndrome. Stress affects GI motility, faecal transit and visceral pain sensitivity. Additionally, permeability and function of the gut epithelium, which acts as a barrier between the external environment and the body's internal milieu is altered by stress. However, the effects of an enhanced stress response on colonic morphology require further investigation. We have used two animal models of stress and anxiety, the maternally separated (MS) and Wistar Kyoto (WKY) rats to examine colonic morphology. These rats exhibit increased anxiety behaviours, visceral hypersensitivity and increased stress-induced defecation in the open field arena. At a morphological level, increased mucus secretion and an associated elevation in the number of mucosal goblet cells was observed in the high anxiety rats. Additionally, the mucosal layer was flattened in MS and WKY rats, a finding indicative of mild mucosal damage. Furthermore, the muscular layer of the distal colon in these animals was thickened, an observation that may have implications for faecal transit and visceral pain perception. This study provides evidence of altered colonic function and morphology in two animal models with a heightened response to stress.

Transient receptor potential vanilloid-1 (TRPV1) and ankyrin-1 (TRPA1) participate in visceral hyperalgesia in chronic water avoidance stress rat model

Stressfull life events have powerful influences on visceral perception of certain IBS patients. In the present study, we aimed to examine the involvement of TRPV1 and TRPA1 in the stress-induced visceral hyperalgesia. Rats were exposed to 1-h water avoidance stress (WAS) daily for 10 consecutive days. The abdominal withdrawal reflex (AWR) to colorectal distension was assessed at the end of the 10-day period. Western-blotting analysis was applied to investigate the alterations of TRPV1 and TRPA1 in the colonic afferent dorsal root ganglia (DRG). Compared with control rats, the WAS-treated rats demonstrated a significant increase in the AWR with the pressure > or = 40 mm Hg (P < 0.05). Meanwhile, in the WAS-treated rats, western-blotting analysis showed significant upregulation of TRPV1 and TRPA1 in the colonic afferent DRG. The results indicate that WAS could induce the upregulation of TRPV1 and TRPA1 in the colonic afferent DRG, and both receptors may be candidate molecules involved in the stress-induced visceral hyperalgesia in rats.

Peripheral infusion of nociceptin/orphanin FQ influences the response of rat gastric and colonic mucosa to repeated stress

The 17-amino acid peptide nociceptin/orphanin FQ (N/OFQ) plays a role in the regulation of stress responses and of emotional disorders. The objective of this study is to evaluate whether long-term peripheral N/OFQ could dose- and time-dependently influence the responses to repeated cold-restraint stress on the rat gastric and colonic mucosa. Rats were exposed to cold-restraint stress for 3h per day for 1, 2 and 3 consecutive days. N/OFQ was administered at doses of 0.1, 1 and 10 microg/kg/h via Alzet osmotic minipumps. In the gastric fundus, N/OFQ exerted dose-dependent beneficial effects against acute and repeated stress but, after prolonged treatment, became damaging in non-stressed rats. In the distal colon, N/OFQ exerted a protective effect against damage by acute and repeated stress with no influence on epithelial integrity in non-stressed rats. In both regions, the peptide itself dose- and time-dependently reduced intraepithelial mucins. The reduction in mucin content caused by stress was effectively counteracted by N/OFQ, 0.1 microg/kg/h, in the distal colon only. N/OFQ did not modify basal mucosal cell proliferation. The peptide at 0.1 and 1 microg/kg/h had no influence while at 10 microg/kg/h abolished stress-induced increase in cell proliferation. The present results provide evidence that N/OFQ is implicated in the regulation of resting and stress-challenged mucosal integrity and activity of mucin-producing cells.

Management of stress in inflammatory bowel disease: a therapeutic option?

There is increasing evidence that psychological stress and associated mood disorders are linked with, and can adversely affect the course of, inflammatory bowel disease (IBD). Unfortunately, owing to methodological difficulties inherent in undertaking appropriately targeted and blinded trials, there are limited high-quality data regarding the effects on IBD of interventions aimed to ameliorate stress and mood disorders. Nevertheless, patients want psychological intervention as well as conventional medical strategies. Emerging trial evidence supports the suggestion that psychologically orientated therapy may ameliorate IBD-associated mood disorders, but there are no strong data as of yet to indicate that stress management has a beneficial effect on the activity or course of IBD. As yet, which, when and how interventions targeted at psychological stress and mood disturbances should be offered to individual patients with IBD is not clear.

Corticotropin-releasing hormone and mast cells in the regulation of mucosal barrier function in the human colon

Corticotropin-releasing hormone (CRH) is an important neuro-endocrine mediator of the stress response. Local effects of CRH in the intestinal mucosa have become evident in recent years. We showed that CRH activates CRH receptor subtypes R1 and R2 on subepithelial mast cells, thereby inducing increased transcellular uptake of protein antigens in human colonic biopsies in Ussing chambers. Ongoing studies also implicate local cholinergic signaling in regulation of macromolecular permeability in the human colon. Since increased uptake of antigenic molecules is associated with mucosal inflammation, our findings may have implications for understanding stress-related intestinal disorders.

Physiological and pathophysiological functions of intestinal mast cells

The normal gastrointestinal (GI) mucosa is equipped with mast cells that account for 2-3% of lamina propria cells under normal conditions. Mast cells are generally associated with allergic disease, and indeed, food allergy that manifests in the GI tract is usually mast cell dependent. On the other hand, mast cells have a number of physiological functions in the GI tract, namely regulatory functions such as control of blood flow and coagulation, smooth muscle contraction and peristalsis, and secretion of acid, electrolytes, and mucus by epithelial cells. One of the most intriguing functions of intestinal mast cells is their role in host defense against microbes like bacteria, viruses, or parasites. Mast cells recognize microbes by antibody-dependent mechanisms and through pattern-recognition receptors. They direct the subsequent immune response by attracting both granulocytes and lymphocytes to the site of challenge via paracrine cytokine release. Moreover, mast cells initiate, by releasing proinflammatory mediators, innate defense mechanisms such as enhanced epithelial secretion, peristalsis, and alarm programs of the enteric nervous This initiation can occur in response to a primary contact to the microbe or other danger signals, but becomes much more effective if the triggering antigen reappears and antibodies of the IgE or IgG type have been generated in the meantime by the specific immune system. Thus, mast cells operate at the interface between innate and adaptive immune responses to enhance the defense against pathogens and, most likely, the commensal flora. In this respect, it is important to note that mast cells are directly involved in controlling the function of the intestinal barrier that turned out to be a crucial site for the development of infectious and immune-mediated diseases. Hence, intestinal mast cells perform regulatory functions to maintain tissue homeostasis, they are involved in host defense mechanisms against pathogens, and they can induce allergy once they are sensitized against foreign antigens. The broad spectrum of functions makes mast cells a fascinating target for future pharmacological or nutritional interventions.

Postinfectious irritable bowel syndrome

Approximately 1 in ten patients with irritable bowel syndrome (IBS) believe their IBS began with an infectious illness. Prospective studies have shown that 3% to 36% of enteric infections lead to persistent new IBS symptoms; the precise incidence depends on the infecting organism. Whereas viral gastroenteritis seems to have only short-term effects, bacterial enteritis and protozoan and helminth infections are followed by prolonged postinfective IBS (PI-IBS). Risk factors for developing PI-IBS include, in order of importance, prolonged duration of initial illness, toxicity of infecting bacterial strain, smoking, mucosal markers of inflammation, female gender, depression, hypochondriasis, and adverse life events in the preceding 3 months. Age older than 60 years might protect against PI-IBS, whereas treatment with antibiotics has been associated with increased risk. The mechanisms that cause PI-IBS are unknown but could include residual inflammation or persistent changes in mucosal immunocytes, enterochromaffin and mast cells, enteric nerves, and the gastrointestinal microbiota. Adverse psychological factors contribute to persistent low-grade inflammation. The prognosis for patients with PI-IBS is somewhat better than for those with unselected IBS, but PI-IBS can still take years to resolve. There are no specific treatments for PI-IBS; these should be tailored to the predominant bowel disturbance, which is most frequently diarrhea.

Intestinal dendritic cells and epithelial barrier dysfunction in Crohn's disease

Crohn's disease (CD) is a chronic gastrointestinal inflammatory disorder considered to be the result of an inappropriate and exaggerated mucosal immune reaction to yet undefined triggers from the gut flora in genetically predisposed individuals. This inflammatory phenomenon has been characterized by an adaptive T-cell response in addition to an abnormal function of the innate immune system. Dendritic cells (DCs) are constituents of this innate system, inducing T-cell activation via antigen presentation. In the gut, mucosal DCs are separated from the luminal milieu by a monolayer of cylindrical epithelial cells that forms an anatomical and physiological barrier that controls the normal traffic of antigens between both compartments. An imbalance of colonic and ileal DC distribution in tissues from CD patients as well as functional differences between DCs isolated from normal and diseased intestinal samples have been demonstrated. Moreover, a gut barrier defect in the para- and transepithelial routes in addition to a significant reduction in the intestinal secretion of epithelial products involved in barrier function has been well documented in CD. Therefore, this may expose the diseased mucosa to overwhelming amounts of antigens, resulting in abnormal DC activation and a subsequent imbalance in their distribution. In conclusion, this review provides a summary of relevant progress in CD, intestinal epithelial permeability, and DCs highlighting a potential relationship between increased epithelial permeability and abnormal DC distribution during the pathogenesis of intestinal inflammation.

The functional-organic dichotomy: postinfectious irritable bowel syndrome and inflammatory bowel disease-irritable bowel syndrome

Gastroenterologists often encounter situations when the clinical and pathophysiological features that typically distinguish functional from organic disorders overlap. This "blurring of boundaries" can occur with post-infectious irritable bowel syndrome (PI-IBS), a subset of IBS and a newly described entity IBD-IBS. The key associating features include pain and usually diarrheal symptoms that are disproportionate to the observed pathology, microscopic inflammation, and often a co-association with psychological distress. A previous initiating gastrointestinal infection is required for PI-IBS and assumed for IBD-IBS. Using this perspective we discuss the clinical and pathophysiological features of PI-IBS and IBD-IBS and the growing evidence for the overlapping features of these two disorders in terms of alteration of gut flora, immune dysregulation, and role of stress. A unifying model of PI-IBS and IBD-IBS is proposed that may have important clinical and research implications. It obligates us to reframe our understanding of illness and disease from the dualistic biomedical model into a more integrated biopsychosocial (BPS) perspective.

The effect of chronic variable stress on bowel habit and adrenal function in rats

BACKGROUND AND AIM

Increased colonic motility is a well-known stress response and corticotropin releasing hormone plays an important role in this response, but sequential change of bowel habit and adrenal function during chronic stress has not been reported. The objective of this study was to evaluate the effect of chronic stress on bowel habit and adrenal function.

METHODS

Male Sprague-Dawley rats were exposed to chronic variable stress (CVS) for 6 weeks. We measured daily the number and weight of pellets and weekly urinary corticosterone. After 6 weeks of experiment, visceromotor response (VMR) to colorectal distention (CRD), serum corticosterone and adrenal glands weight were measured.

RESULTS

The number and weight of pellets in CVS rats was greater than those of the control rats initially and decreased during the later period. However, CVS rats showed continuously exaggerated daily variation of pellet number than control rats to the end of experimental period. Urinary corticosterone was increased in CVS rat until the fifth week, but urine and serum corticosterone were not statistically different between groups at the sixth week. However, the relative weight of adrenal glands was higher in CVS rats at the sixth week. CVS rats showed exaggerated VMR to CRD than the control rats.

CONCLUSIONS

The prolonged and variable stress to rats induced sustained bowel habit dysfunction and visceral hypersensitivity without adaptation. Chronic stress also increased adrenal activity from the early phase and finally caused adrenal hypertrophy with relatively decreased activity. But adrenal change was not parallel to bowel habit change and it remains to be seen whether adrenal dysfunction is directly related to bowel habit dysfunction.

Stress neuropeptides evoke epithelial responses via mast cell activation in the rat colon

BACKGROUND

Previously, we showed that corticotropin-releasing factor (CRF) injected i.p. mimicked epithelial responses to stress, both stimulating ion secretion and enhancing permeability in the rat colon, and mast cells were involved. However, the ability of CRF-sensitive mucosal/submucosal loops to regulate intestinal barrier and the participation of resident mast cells are unclear.

METHODS

We examined colonic epithelial responses to stress-like peptides in Wistar-Kyoto (WKY), and mast cell-deficient (Ws/Ws) and their +/+ littermate control rats in distal segments mounted in Ussing chambers. Short-circuit current (ion secretion), flux of horseradish peroxidase (macromolecular permeability), and the release of rat mast cell protease II were measured in response to CRF [10(-6) to 10(-8)M] or sauvagine [10(-8) to 10(-10)M] in tissues pretreated with astressin, doxantrazole, or vehicle.

RESULTS

Stress-like peptides (sauvagine > CRF) induced a dose-dependent increase in short-circuit current (maximal at 30 min), and significantly enhanced horseradish peroxidase flux and protease II release in WKY. Epithelial responses were inhibited by both astressin and doxantrazole, and significantly reduced in tissues from Ws/Ws rats.

CONCLUSION

The stress mediators CRF and sauvagine modulate barrier function in the rat colon acting on mucosal/submucosal CRF receptor-bearing cells, through mast cell-dependent pathways.

Corticotropin-releasing hormone receptor 1 antagonist blocks colonic hypersensitivity induced by a combination of inflammation and repetitive colorectal distension

Gastroenteritis is one of the risk factors for developing irritable bowel syndrome (IBS). However, the precise mechanism of postinfectious IBS is still unknown. We tested the hypothesis that a combination of previous inflammation and repetitive colorectal distention (CRD) makes the colon hypersensitive and that treatment with a corticotropin-releasing hormone receptor 1 (CRH-R1) antagonist blocks this colonic hypersensitivity. Rats were pretreated with vehicle or 2,4,6-trinitrobenzene sulphonic acid (TNBS) 6 weeks before CRD. For the CRD experiment, the colorectum was distended once a day for six consecutive days. The CRH-R1 antagonist (CP-154,526, 20 mg kg(-1)) or vehicle was injected subcutaneously 30 min before CRD. Visceral perception was quantified as visceromotor response (VMR) using an electromyograph. For histological examination, the rats were killed on the last day of CRD experiment, and haematoxylin and eosin-staining of colon segments was performed. Although from the first to the third day of CRD, VMRs increased in both the vehicle-treated rats and TNBS-treated rats, they were significantly higher in TNBS-treated rats than those in vehicle-treated controls. On the fifth day of CRD, however, VMRs in the vehicle-treated rats were significantly greater than those in TNBS-treated rats. Pretreatment of rats with CP-154,526 significantly attenuated the increase in VMR induced by repetitive CRD with previous inflammation. Finally, we found that repetitive CRD and repetitive CRD after colitis induced visceral inflammation. These results indicate that a combination of previous inflammation and repetitive CRD induces visceral hypersensitivity and that a CRH-R1 antagonist attenuates this response in rats.

Psychological stress reactivates dextran sulfate sodium-induced chronic colitis in mice

Inflammatory bowel disease (IBD) is a chronic condition with alternating active and quiescent phases of inflammation. Stress has been suggested as a factor triggering a relapse of IBD. We investigated the role of repetitive psychological stress [water avoidance stress (WAS)] in reactivating colonic inflammation in a murine model of dextran sulfate sodium (DSS)-induced chronic colitis. Colitis was induced in C57BL/6 female mice by exposure to 3% DSS (5 days). During chronic inflammation(day 34), mice underwent repetitive WAS (1 h/day/7 days) and were given a sub-threshold concentration of DSS (1%, 5 days)or normal water to drink. At euthanasia (day 40), inflammatory parameters were assessed (colon inflammatory score, levels of inflammatory markers and histology). Mice with chronic colitis exposed to WAS had higher macroscopic and microscopic colonic inflammatory scores and levels of inflammatory markers (mainly IL-1beta, IL12p40 and CCL5) than non-stressed mice. Inflammatory responses were further enhanced by the presence of a sub-threshold concentration of DSS (1%). In mice without chronic inflammation, neither WAS nor 1% DSS, individually or in combination, elicited any inflammation. Hence stress, per se, reactivates a quiescent chronic inflammation, but does not initiate inflammation in healthy mice. Stress should be regarded as an environmental factor triggering IBD relapses in humans.

Chronic peripheral administration of corticotropin-releasing factor causes colonic barrier dysfunction similar to psychological stress

Chronic psychological stress causes intestinal barrier dysfunction and impairs host defense mechanisms mediated by corticotrophin-releasing factor (CRF) and mast cells; however, the exact pathways involved are unclear. Here we investigated the effect of chronic CRF administration on colonic permeability and ion transport functions in rats and the role of mast cells in maintaining the abnormalities. CRF was delivered over 12 days via osmotic minipumps implanted subcutaneously in wild-type (+/+) and mast cell-deficient (Ws/Ws) rats. Colonic segments were excised for ex vivo functional studies in Ussing chambers [short-circuit current (Isc), conductance (G), and macromolecular permeability (horseradish peroxidase flux)], and analysis of morphological changes (mast cell numbers and bacterial host-interactions) was determined by light and electron microscopy. Chronic CRF treatment resulted in colonic mucosal dysfunction with increased Isc, G, and horseradish peroxidase flux in+/+but not in Ws/Ws rats. Furthermore, CRF administration caused mast cell hyperplasia and abnormal bacterial attachment and/or penetration into the mucosa only in+/+rats. Finally, selective CRF agonist/antagonist studies revealed that stimulation of CRF-R1 and CRF-R2 receptors induced the elevated secretory state and permeability dysfunction, respectively. Chronic CRF causes colonic barrier dysfunction in rats, which is mediated, at least in part, via mast cells. This information may be useful in designing novel treatment strategies for stress-related gastrointestinal disorders.

The leukotriene d4 receptor antagonist, montelukast, inhibits mast cell degranulation in the dermis induced by water avoidance stress

Cysteinyl leukotrienes play a part in inflammatory reactions such as asthma and inflammatory bowel diseases. The leukotrienes exert their actions by binding to and activating various receptors. Montelukast, a leukotriene receptor antagonist, which is used in the treatment of asthma has been shown to be effective in inhibiting the action or formation of leukotrienes. Many skin disorders, such as atopic dermatitis and psoriasis, worsen during stress and seem to be related to infiltration and activation of mast cells that are releasing vasoactive and pro-inflammatory mediators. The aim of the present study was to investigate the effects of montelukast on the degranulation of mast cells in the dermis that is induced by water avoidance stress (WAS). Wistar albino rats were divided into four groups of 8 animals each. Control rats were injected with (1) the vehicle solution or (2) the montelukast solution in the absence of WAS. (3) the WAS group of rats was administered vehicle solution following WAS exposure for 2h daily for 5 days. (4) The WAS+ML group was administered montelukast 10mg/kg; i.p. following WAS exposure for 2h daily for 5 days. Dermal mast cell numbers were determined with toluidine blue and tryptase immunohistochemistry and observed using a light microscope. Numbers of both granulated and degranulated mast cells were significantly increased in the WAS group when compared to control rats. Montelukast treatment decreased the number of both mature granulated and degranulated mast cells in rats subjected to WAS. In conclusion, chronic montelukast treatment reduced WAS-induced infiltration and activation of mast cells in the dermis and may provide a useful therapeutic option in stress-induced skin disorders.

Maladaptive intestinal epithelial responses to life stress may predispose healthy women to gut mucosal inflammation

BACKGROUND & AIMS

Irritable bowel syndrome (IBS), a highly prevalent disorder among women, has been associated with life stress, but the peripheral mechanisms involved remain largely unexplored.

METHODS

A 20-cm jejunal segment perfusion was performed in 2 groups of young healthy women, equilibrated by menstrual phase, experiencing either low (LS; n = 13) or moderate background stress (MS; n = 11). Intestinal effluents were collected every 15 minutes, for 30 minutes under basal conditions, and for 1 hour after cold pain stress. Cardiovascular and psychological response, changes in circulating stress and gonadal hormones, and epithelial function (net water flux, albumin output and luminal release of tryptase and alpha-defensins) to cold stress were determined.

RESULTS

Cold pain induced a psychological response stronger in the MS than in the LS group, but similar increases in heart rate, blood pressure, adrenocorticotrophic hormone, and cortisol, whereas estradiol and progesterone remained unaltered. Notably, the jejunal epithelium of MS females showed a chloride-related decrease in peak secretory response (Delta[15-0 minutes]: LS, 97.5 [68.4-135.0]; MS, 48.8 [36.6-65.0] microL/min/cm; P < .001) combined with a marked enhancement of albumin permeability (LS(AUC), 6.35 [0.9-9.6]; MS(AUC), 13.97 [8.3-23.1] mg/60 min; P = .008) after cold stress. Epithelial response in both groups was associated with similar increases in luminal tryptase and alpha-defensins release.

CONCLUSIONS

Increased exposure to life events determines a defective jejunal epithelial response to incoming stimuli. This abnormal response may represent an initial step in the development of prolonged mucosal dysfunction, a finding that could be linked to enhanced susceptibility for IBS.

Leukotriene D4 receptor antagonist montelukast alleviates water avoidance stress-induced degeneration of the gastrointestinal mucosa

We investigated the role of montelukast (ML), a cysteinyl leukotriene-1 receptor antagonist, on the water avoidance stress (WAS)-induced degeneration of the rat gastric, ileal and colonic mucosa. One group of Wistar albino rats were exposed to chronic WAS (WAS group) 2h daily for 5 days. Another group was administered ML (10mg/kg; i.p.; WAS+ML group) following every WAS exposure for 5 days. Control rats were injected with the vehicle solution only. The stomach, ileum and colon were dissected and investigated for histopathological changes with a light microscope as well as for topographical changes with a scanning electron microscope. The levels of malondialdehyde (MDA, a biomarker of oxidative damage) and glutathione (GSH, a biomarker of protective oxidative injury) were also determined in all dissected tissues. In the WAS group, the stomach epithelium showed ulceration in some areas, dilatations of the gastric glands, degeneration of gastric glandular cells, and prominent congestion of the capillaries. In a similar fashion, degenerated epithelium and severe vascular congestions were observed in the ileum and colon. In all the tissues dense inflammatory cell infiltration and mast cell degranulation in mucosa were observed. The levels of MDA were significantly increased whereas those of GSH were significantly decreased in all test tissues in the WAS group compared to the control group. The morphology of gastric, ileal and colonic mucosa in WAS+ML group showed a significant amelioration showing a reduction in inflammatory cell infiltration and mast cell degranulation. Increased MDA and decreased GSH levels in the WAS group were also ameliorated with ML treatment. Based on the results, ML supplement seems attenuated inflammatory effects of WAS induction in gastrointestinal mucosa.